1. Field of the Invention
The present invention relates generally to heat exchangers for motor vehicles and, more specifically, to a folded tube and method of making same for a heat exchanger in a motor vehicle.
2. Description of the Related Art
It is known to provide a tube for a heat exchanger such as a condenser in an air conditioning system of a motor vehicle. The tube typically carries a first fluid medium in contact with its interior while a second fluid medium contacts its exterior. Typically, the first fluid medium is a liquid or a two-phase liquid and gas mixture and the second fluid medium is a gas. Where a temperature difference exists between the first and second fluid mediums, heat will be transferred between the two via heat conductive walls of the tube.
It is also known to provide corrugated fins or ribs in the interior of the tube to increase the surface area of conductive material available for heat transfer to cause turbulence of the fluid carried in the interior of the tube and to increase the burst strength of the tube. One known method of making such a tube is to physically insert a corrugated fin into the generally flattened tube after the tube has been manufactured. This is an extremely difficult process since the corrugated fin to be inserted into the tube is extremely thin and subject to deformation during the insertion process.
Another known method of forming a tube for a heat exchanger is to extrude the tube in an extrusion process. In this construction, internal ribs are formed during the extrusion. However, these extruded tubes are relatively expensive to produce.
Yet another known method of forming a tube for a heat exchanger is to provide a flat, elongated sheet with lugs and the ends of the sheet are folded to form the tube. The ends of the tube are then brazed. An example of such a tube is disclosed in U.S. Pat. No. 5,386,629. In this patent, the tube may have flow paths between the lugs. However, the quality of the folded tube to header joints is related to how small the outside web shoulders can be with the smaller the better to prevent leakage.
It is desirable to provide a folded tube with very small outside web shoulder radii. It is also desirable to provide a method to achieve small web shoulder for a folded tube. It is further desirable to provide a folded tube for enhancing heat transfer of the heat exchanger. Therefore, there is a need in the art to provide a folded tube for a heat exchanger of a motor vehicle that achieves these desires.